Ah, but what does it matter? What are the differences between the 32- and 64-bit versions of Windows (often known as "x86" and "x64," respectively), and if you're buying a new PC, which one should you choose?

Short answer: for most home users, 32-bit Windows is fine and dandy. If you're more of a power user, opt for 64-bit (which is increasingly common on new PCs anyway, so you may not even have a choice).

The key consideration is RAM: 32-bit Windows can address only 3.5GB of it, while 64-bit Windows can address 4GB or more. Because so many new PCs come with at least 4GB, that's why you're seeing Windows x64 as the default OS.

For more than 20 years, Rick Broida has written about all manner of technology, from Amigas to business servers to PalmPilots. His credits include dozens of books, blogs, and magazines. He sleeps with an iPad under his pillow.